vc-git doesn't select current revision in vc-print-log

["Chris Moore" <christopher.ian.moore@gmail.com>]

Using "C-x v l" to show a file's revision history is supposed to
select the current version in the log, but for git-controlled files it
leaves point at the end.

This is because (log-view-goto-rev rev) is called with REV bound to a
branch name ("master", or whatever), but log-view-goto-rev can only
match on the SHA1 hashes.

It turns out that the current revision is always the first one in the
list, since vc-print-log lists from the currently selected version
backwards, so adding the following to vc-git.el fixes the problem:

(defun vc-git-show-log-entry (rev)
  (goto-char (point-min))
  (log-view-msg-next))

I also noticed that reloading vc-git.el isn't enough to get VC to
notice the new function.  vc-arch.el has this in it:

;; Clear up the cache to force vc-call to check again and discover
;; new functions when we reload this file.
(put 'Arch 'vc-functions nil)

perhaps vc-git.el would benefit from the same (with 'Git instead of
'Arch, of course).

Chris.